An element ${}^{35}${17}\text X \space \text{and} \space {}^{40}{20}\text Y are to be placed in the periodic table.

(a) In which group and period will X and Y be placed?

(b) State whether they are :

1. Metal or non-metal.
2. Oxidising agent or reducing agent.

(c) Can these two atoms combine to form a compound ? If yes, can you predict 3 properties of this compound?

(d) Write the formula of their oxide.

Given elements are:

${}^{35}${17}\text X \space \text{and} \space {}^{40}{20}\text Y

So, atomic number of X = 17 and atomic number of Y = 20.

(a) Group and period of X and Y

For X:

Atomic number = 17
Electronic configuration = 2, 8, 7

Since X has 3 shells, it belongs to Period 3. Since X has 7 valence electrons, it belongs to Group 17.

For Y:

Atomic number = 20
Electronic configuration = 2, 8, 8, 2

Since Y has 4 shells, it belongs to Period 4. Since Y has 2 valence electrons, it belongs to Group 2.

(b) Nature of X and Y

1. X is a non-metal, while Y is a metal.
2. X is an oxidising agent, as it tends to gain electrons.
   Y is a reducing agent, as it tends to lose electrons.

(c) Formation and properties of compound:

Yes, X and Y can combine to form a compound.

Y loses two electrons to form a Y²⁺ ion. Each X atom gains one electron to form an X^- ion.

Hence, X and Y can combine and form an ionic compound.

Three properties of this compound are:

1. The compound has high melting and boiling point.
2. It conducts electricity in molten or aqueous state.
3. It is soluble in water.

(d) Formula of their oxides:

• Oxide of X ⇒ X₂O₇
  (As X is Chlorine [Cl], hence formula of its oxide will be Cl₂O₇)
• Oxide of Y ⇒ YO
  (As Y is Calcium [Ca], hence formula of its oxide will be CaO)

Explanation:

For X:

X has atomic number 17 and electronic configuration 2, 8, 7. It belongs to Group 17. Its valency with respect to oxygen is 7.

Oxygen has valency 2.

$\text{X}^{7} \quad \text{O}^{2}$

By criss-crossing the valencies, the formula of the oxide of X is:

$\text{X}$2\text{O}7

For Y:

Y has atomic number 20 and electronic configuration 2, 8, 8, 2. It belongs to Group 2. Hence, its valency is 2.

Oxygen also has valency 2.

$\text{Y}^{2} \quad \text{O}^{2}$

By criss-crossing and simplifying, the formula of the oxide of Y is:

$\text{YO}$

Hence, the formulae of their oxides are:

X₂O₇ and YO